Disk device

ABSTRACT

According to one embodiment, a disk device includes a first actuator assembly and a second actuator assembly which are respectively supported by a first bearing unit and a second bearing unit to be rotatable about a support shaft. The first bearing unit includes a first sleeve and a ball bearing. The second bearing unit includes a second sleeve and a ball bearing. The first sleeve includes a first end surface opposed to the second sleeve and an annular first step projecting from the first end surface, and the second sleeve includes a second end surface opposed to the first step with a gap and an annular second step projecting from the second end surface. The second step is opposed to the first step and the first end surface with a gap.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 16/658,975filed Oct. 21, 2019, which is a divisional of application Ser. No.15/998,870 filed Aug. 17, 2018, now patented U.S. Pat. No. 10,490,217,and is based upon and claims the benefit of priority from JapanesePatent Application No. 2018-051493, filed Mar. 19, 2018, the entirecontents of which are incorporated herein by reference.

FIELD

Embodiments described herein relate generally to a disk device includinga head actuator assembly.

BACKGROUND

Hard disk drives (HDDs), as an example of a disk device, comprise, forexample, a magnetic disk disposed in a casing, spindle motor configuredto support and rotate the magnetic disk, actuator assembly supporting amagnetic head, voice coil motor configured to drive the actuatorassembly, and flexible printed circuit unit (hereinafter referred to asFPC unit).

The actuator assembly comprises an actuator block including a pluralityof arms and a unit bearing attached to an attachment hole of theactuator block. To each arm, one or two suspension assemblies supportingthe magnetic head are attached. The unit bearing is, for example, acombination of two ball bearings and a spacer. The bearings are greasedto reduce friction and wearing.

During a seek operation by the actuator assembly, grease or lubricantmay be splashed from between inner and outer rings of the bearings. Thesplashing grease may be leaked or added to the magnetic disk and themagnetic head to cause insufficient flying and crushing of the magnetichead, and thereby results in a great problem such as read/write error.To prevent this, the upper part of the unit bearing is covered with acap and the lower part thereof is covered with a shaft base to blocksplashing grease.

In recent years, storage capacity of HDD is increased, and accordingly,the number of magnetic disks disposed therein is increased. In order todeal with a number of magnetic disks, a so-called dual actuator assemblyincluding two or more actuator assembles is proposed. In the dualactuator assembly, two unit bearings are disposed one-on-another in theaxis direction with a spacer therebetween. In that case, a greasesplashing space (gap) which is difficult to be adjusted by the cap andshaft base is formed between two unit bearings. Thus, grease splash fromthe unit bearings may possibly be increased.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a hard disk drive (HDD) of a firstembodiment with a top cover thereof detached.

FIG. 2 is a perspective view of a head actuator assembly and a substrateunit of the HDD.

FIG. 3 is a cross-sectional view of the head actuator assembly.

FIG. 4 is a perspective view of an actuator block of the head actuatorassembly in a partly broken manner.

FIG. 5 is a cross-sectional view of the actuator block of the headactuator assembly.

FIG. 6 is a cross-sectional view showing a gap between bearing units inan enlarged manner.

FIG. 7 is a perspective view of an actuator block of a head actuatorassembly in an HDD of a second embodiment.

FIG. 8 is a cross-sectional view of the actuator block of the headactuator assembly.

FIG. 9 is a cross-sectional view of a gap between the bearing units inan enlarged manner.

DETAILED DESCRIPTION

Various embodiments will be described hereinafter with reference to theaccompanying drawings. In general, according to one embodiment, a diskdevice comprises a disk shaped recording medium including a recordinglayer; a first actuator assembly including a first actuator blockrotatably supported on a support shaft via a first bearing unit, asuspension assembly extending from the first actuator block, and amagnetic head supported by the suspension assembly; and a secondactuator assembly including a second actuator block rotatably supportedon the support shaft via a second bearing unit, a suspension assemblyextending from the first actuator block, and a magnetic head supportedby the suspension assembly. The first bearing unit comprises a firstsleeve fixed to the first actuator block and located around the supportshaft in a coaxial manner, and one or more ball bearings disposedbetween the support shaft and the first sleeve. The second bearing unitcomprises a second sleeve fixed to the second actuator block and locatedaround the support shaft in a coaxial manner, and one or more ballbearings disposed between the support shaft and the second sleeve. Thefirst sleeve includes a first end surface opposed to the second sleeve,and an annular first step which projects from the first end surface andis located coaxial with the support shaft. The second sleeve includes asecond end surface opposed to the first step with a gap therebetween,and an annular second step which projects from the second end surfaceand is located coaxial with the support shaft, wherein the second stepoverlaps the first step in a radial direction of the first sleeve and isopposed to the first step and the first end surface with a gaptherebetween.

The disclosure is merely an example, and proper changes within thespirit of the invention, which are easily conceivable by a person withordinary skill in the art, are included in the scope of the invention asa matter of course. In addition, in some cases, in order to make thedescription clearer, the widths, the thicknesses, the shapes, etc., ofthe respective parts are schematically illustrated in the drawings,compared to the actual modes. However, the schematic illustration ismerely an example, and adds no restrictions on the interpretation of thepresent invention. Further, in the specification and drawings, the sameelements as those described in connection with preceding drawings aregiven the same reference numbers, and a detailed description thereof isomitted as appropriate.

First Embodiment

A hard disk drive (HDD) according to a first embodiment as a disk drivewill be explained.

FIG. 1 is a perspective view showing the HDD of the first embodimentwith a top cover detached.

HDD comprises a flat and substantially rectangular casing 10. The casing10 includes a rectangular box-shaped base 12 upper surface of which isopened and a top cover 14. The top cover 14 is fixed to the base 12 witha plurality of screws 13 to block the upper end opening of the base 12.The base 12 includes a rectangular bottom wall 12 a opposed to the topcover 14 with a gap therebetween, and side walls 12 b standing along theperiphery of the bottom wall 12 a. The bottom wall 12 a and the sidewalls 12 b are formed integrally of aluminum, for example. The top cover14 is formed in a rectangular plate-shape with stainless, for example.The top cover 14 is fixed on the side walls 12 b of the base 12 withscrews to close the upper end opening of the base 12.

The casing 10 accommodates a plurality of magnetic disks 18 as recordingmedia and spindle motor 19 which supports and rotates the magnetic disks18. The spindle motor 19 is disposed on the bottom wall 12 a. Eachmagnetic disk 18 is formed with a diameter of 88.9 mm (3.5 inch) andincludes a magnetic recording layer in the upper surface and/or thelower surface thereof. Each magnetic disk 18 is fit to a hub (which isnot shown) of the spindle motor 19 in a coaxial manner and is clamped bya clamp spring 20 to be fixed to the hub. Thus, each magnetic disk 18 issupported in a position parallel to the bottom wall 12 a of the base 12.The magnetic disk 18 are rotated by the spindle motor 19 in a certainrotation rate.

Note that, as shown in FIG. 1, seven magnetic disks 18 are disposed inthe casing 10 in the present embodiment; however, the number of themagnetic disks 18 is not limited thereto.

The casing 10 accommodates a plurality of magnetic heads 17 which recordand resume data to/from the magnetic disk 18 and a head actuatorassembly which supports the magnetic heads 17 in a movable manner withrespect to the magnetic disk 18. In the present embodiment, the headactuator assembly is formed as a dual actuator assembly including aplurality of actuator assemblies such as a first actuator assembly 22Aand a second actuator assembly 22B.

Furthermore, the casing 10 accommodates a voice coil motor (VCM) 24which rotates and positions the first and second actuator assemblies 22Aand 22B, a ramp loading mechanism 25 which keeps the magnetic heads 17apart from the magnetic disk 18 in an unloaded position when themagnetic heads 17 move to the outermost periphery of the magnetic disk18, and substrate unit (FPC unit) 21 on which electronic components suchas a conversion connector are mounted.

On the outer surface of the bottom wall 12 a of the base 12, a printedcircuit board (not shown) is not shown is fixed with screws. The printedcircuit board controls the operation of the spindle motor 19 and forms acontroller which controls the operation of VCM 24 and magnetic heads 17via the substrate unit 21.

FIG. 2 is a perspective view of a head actuator assembly including adual actuator assembly and an FPC unit, and FIG. 3 is a side view of thedual actuator assembly. As shown in FIGS. 2 and 3, the dual actuatorassembly comprises the first actuator assembly 22A and the secondactuator assembly 22B. The first and second actuator assemblies 22A and22B are layered, and furthermore, are provided to be independentlyrotatable around a common axis (support shaft) 26 which is disposedvertically on the bottom wall 12 a of the base 12. The first and secondactuator assemblies 22A and 22B are formed in substantially the samestructure. In this example, the actuator assembly arranged on the upperside is the first actuator assembly 22A and the actuator assemblyarranged on the lower side is the second actuator assembly 22B.

The first actuator assembly 22A comprises an actuator block (firstactuator block) 29, four arms 30 extending from the actuator block 29,suspension assemblies 32 attached to each arm 30, and magnetic heads 17supported by the suspension assemblies 32. The actuator block 29includes an inner hole 31 and a bearing unit (unit bearing) 50, whichwill be described later, accommodated in the inner hole 31.

In the present embodiment, the actuator block 29 and four arms 30 areformed integrally with aluminum or the like, and form a so-called Eblock. The arm 30 is formed in a slender flat plate shape and extends ina direction orthogonal to the support shaft 26. Four arms 30 areprovided in parallel to one another at certain intervals.

The first actuator assembly 22A includes a support frame 34 extendingfrom the actuator block 29 in a direction opposite to the arms 30. Avoice coil 36 which is a part of the VCM 24 is supported by the supportframe 34. As shown in FIGS. 1 and 2, the voice coil 36 is positionedbetween a pair of yokes disposed in the base 12 and forms the VCM 24with the yokes 38 and a magnet 39 fixed to one of the yokes 38.

As shown in FIGS. 2 and 3, the first actuator assembly 22A includesseven suspension assemblies 32 which are attached to extending ends ofthe arms 30. The suspension assemblies 32 include up-head suspensionassemblies supporting the magnetic heads 17 upwardly and down-headsuspension assemblies supporting the magnetic head 17 downwardly. Theup-head suspension assembly and the down-head suspension assembly havethe same structure while the former one faces upward and the latter onefaces downward. In the present embodiment, a down-head suspensionassembly 32 is attached to the uppermost arm 30, and an up-headsuspension assembly 32 and a pair of the up-head and down-headsuspension assemblies is attached to each of the other three arms 30.

Each suspension assembly 32 comprises a substantially rectangular baseplate, load beam formed of a plate spring, and a band-shaped flexure(wiring member) 40. The flexure 40 is attached to the surface of theload beam and the base plate and extends from the side edge of the baseplate outwardly along the arm 30 to the proximal end of the arm 30(actuator block 29). A displaceable gimbal (elastic supporter) isprovided at the distal end of the flexure 40 positioned on the loadbeam, and the magnetic head 17 is mounted on the gimbal. The wirings offlexure 40 are electrically connected to the magnetic head 17. Note thatthe magnetic head 17 includes a write element and a read element whichare not shown.

The flexure 40 include a connection end 41 provide with the extendingend. The connection end 41 is provided with a plurality of connectionterminals which are not shown. The connection end 41 is connected to theFPC provided on the side surface of the actuator block 29, which will bedescribed later.

On the other hand, the second actuator assembly 22A is formed similarlyto the first actuator assembly 22A. That is, the second assembly 22Bcomprises an actuator block (second actuator block) 29 including abearing unit (second bearing unit) 50, four arms 30 extending from theactuator block 29, seven suspension assemblies 32 attached to the arms30, the magnetic heads 17 supported by the suspension assemblies 32, andvoice coil 36 attached to a support frame 34. In the second actuatorassembly 22B, an up-head suspension assembly 32 is attached to thelowermost arm 30, and a pair of up-head and down-head suspensionassemblies 32 are attached to each of the other three arms 30. Thesecond actuator assembly 22B is rotatably supported by the support shaft26 via the bearing unit 50. Furthermore, the voice coil 36 of the secondactuator assembly 22B is positioned between a pair of yokes 38 disposedin the base 12 and forms the VCM 24 with the yokes 38 and a magnet 39fixed to one of the yokes 38.

Note that the VCM 24 driving the first actuator assembly 22A and the VCM24 driving the second actuator assembly 22B are provided independently.Thus, the first actuator assembly 22A and the second actuator assembly22B can drive (rotate) independently.

As shown in FIG. 2, the FPC unit 21 includes, integrally, asubstantially rectangular base 42, two band-shaped relays 44 extendingfrom one side edge of the base 42, and two joint portions 46 providedsuccessively at the distal ends of the relays 44. The base 42, relays44, and joint portions 46 are formed of flexible printed circuit board(FPC). The flexible printed circuit board includes an insulating layerformed of polyimide or the like, a conductive layer formed on theinsulating layer to form a plurality of wirings, connection pads, andthe like, and a protection layer covering the conductive layer.

On the base 42, electronic components such as a conversion connector anda plurality of condensers which are not shown are mounted and areelectrically connected to the wirings which are not shown. A metal plate45 functioning as a reinforcement plate is added to the base 42. Tworelays 44 extend from the side edge of the base 42 to the first andsecond actuator assemblies 22A and 22B. The joint portion 46 provided atthe extending end of the relay 44 is each adhered to one side surface(mount surface) of the actuator block 29 via a backing plate which isnot shown, and furthermore, is fixed to the amount surface with fixationscrews.

As shown in FIGS. 2 and 3, the connection end 41 of the flexure 40 isconnected to each joint portion 46 and is electrically connected to thewirings of the joint portion 46. A head IC (head amplifier) 48 ismounted on the joint portion 46 and the head IC 48 is connected to theconnection end 41 and the base 42 via the wirings. Furthermore, thejoint portion 46 includes a connection pad 49 to which the voice coil 36is connected.

The seven magnetic heads 17 of the first actuator assembly 22A are eachelectrically connected to the base 42 via the wirings of the flexure 40,the connection end 41, the joint portion 46 of the FPC unit 21, and therelay 44. Similarly, the seven magnetic heads 17 of the second actuatorassembly 22B are each electrically connected to the base 42 via thewirings of the flexure 40, the connection end 41, the joint portion 46of the FPC unit 21, and the relay 44. Furthermore, the base 60 iselectrically connected to the printed circuit board on the bottomsurface side of the casing 10 via the conversion connector.

Then, the bearing unit of the first actuator assembly 22A and the secondactuator assembly 22B will be explained. FIG. 4 shows the actuator blockand the bearing unit in a partly broken manner, and FIG. 5 is across-sectional view of the actuator block and the bearing unit.

As shown, the actuator block 29 of each of the actuator assemblies 22Aand 22B includes an upper end surface 29 a and a lower end surface 29 bwhich are orthogonal to the support shaft 26. The inner hole 31 isformed to penetrate through the actuator block 29 and opens to the upperend surface 29 a and the lower end surface 29 b. The inner hole 31 isformed coaxially with the support shaft 26.

The bearing unit 50 comprises a substantially cylindrical-shaped sleeve(first sleeve) 52 and a pair of ball bearings 54 a and 54 b fit in thesleeve 52. The sleeve 52 has a length in an axis direction, which issubstantially the same as the height of the actuator block 29. The outerdiameter of the sleeve 52 is set to be substantially the same as thediameter of the inner hole 31. The inner diameter of the sleeve 52 isformed greater than the diameter of the support shaft 26. The sleeve 52includes, integrally, an annular projection 53 projecting from themiddle part of the inner peripheral surface of the sleeve 52 toward thecenter of the axis. The sleeve 52 includes an annular first rib (firststep) 56 a projecting from one end surface in the axis direction whichis the upper end surface (first end surface 55 a) in this example, andan annular second rib (second step) 56 b projecting from the other endsurface in the axis direction which is the lower end surface (second endsurface 55 b) in this example. The first rib 56 a is disposed coaxiallywith the sleeve 52 and has an inner diameter substantially the same asthe inner diameter of the sleeve 52. The second rib 56 b is disposedcoaxially with the sleeve 52 and has an inner diameter slightly largerthan the outer diameter of the first rib 56 a. The outer diameter of thesecond rib 56 b is formed slightly smaller than the outer diameter ofthe sleeve 52.

One ball bearing 54 a is disposed in the upper end part of the sleeve 52while the outer race thereof is fit in the inner peripheral surface ofthe sleeve 52. The other ball bearing 54 b is disposed in the lower endpart of the sleeve 52 while the outer race thereof is fit in the innerperipheral surface of the sleeve 52. The projection 53 is positionedbetween the ball bearings 54 a and 54 b and functions as a spacer.

The sleeve 52 of the bearing unit 50 structured as above is fit in theinner hole 31 of the actuator block 29 and is fixed to the actuatorblock 29 with an adhesive agent or the like. The sleeve 52 is positionedcoaxially with the inner hole 31, and the first rib 56 a projectsupwardly from the upper end opening of the inner hole 31. The second rib56 b projects downwardly from the lower end opening of the inner hole31.

The bearing unit (first bearing unit) 50 of the first actuator assembly22A and the bearing unit (second bearing unit) 50 of the second actuatorassembly 22B have the same structure.

The support shaft 26 is formed in a hollow cylindrical shape andincludes an annular flange 26 b formed on the outer periphery of theproximal end thereof. The support shaft 26 is mounted on the bottom wall12 a of the base 12 such that the flange 26 b contacts a boss part ofthe bottom wall 12 a. The support shaft 26 is vertically fixed to thebottom wall 12 a with a fixation bolt which is not shown but is insertedthrough the upper end opening of the support shaft 26 into the bottomwall 12 a.

The second actuator assembly 22B is rotatably supported on the proximalend part of the support shaft 26 via the bearing unit 50. That is, theproximal end part of the support shaft 26 is inserted into the bearingunit 50 and the inner race of the ball bearings 54 a and 54 b fit theouter peripheral surface of the support shaft 26. The lower side ballbearing 54 b is opposed to the flange 26 b of the support shaft 26 witha slight gap therebetween. Thus, the flange 26 b can function as a coverpreventing splash or leakage of grease (lubricant) from the ball bearing54 b.

The first actuator assembly 22A is rotatably supported on the distal endpart of the support shaft 26 via the bearing unit 50. That is, thedistal end part of the support shaft 26 is inserted into the bearingunit 50 and the inner race of the ball bearings 54 a and 54 b fit theouter peripheral surface of the support shaft 26. An annular spacer ring61 is fitted to the outer periphery of the middle part of the supportshaft 26 in the axis direction. The spacer ring 61 is interposed betweenthe upper ball bearing 54 a of the second actuator assembly 22B and thelower ball bearing 54 b of the first actuator assembly 22A. With thespacer ring 61, the upper and lower bearing units 50, that is, the firstand second actuator assemblies 22A and 22B are maintained with a certaingap therebetween.

Note that an annular cap 58 is attached to the outer periphery of theupper end of the support shaft 26. The cap 58 is opposed to the upperball bearing 54 a with a slight gap therebetween. Thus, the cap 58functions as a cover which prevents splash of grease from the bassbearing 54 a.

Hereinafter, the structural elements of the first actuator assembly 22Awill be referred to with “first” before them, and the structuralelements of the second actuator assembly 22B will be referred to with“second” before them.

As shown in FIGS. 4 and 5, the lower end surface 29 b of the firstactuator block 29 and the upper end surface 29 a of the second actuatorblock 29 are opposed to each other in parallel while a slight gap ismaintained therebetween.

The first sleeve 52 of the first bearing unit 50 and the second sleeve52 of the second bearing nit 50 are disposed coaxially and are layeredwith a slight gap therebetween. The first rib 56 a of the second sleeve52 is slid into the inner peripheral side of the second rib 56 b of thefirst sleeve 52, and the first and second ribs 56 a and 56 b overlap ina radial direction of the sleeve, that is, are disposed aside in theradial direction. The first rib 56 a is opposed to the lower end surface(second end surface) 55 b of the first sleeve 52 and the innerperipheral surface of the second rib 56 b with a slight gap between.

The second rib 56 b of the first sleeve 52 is disposed on the outerperipheral side of the first rib 56 a of the second sleeve 52, andfurthermore, projects into the inner hole 31 of the second actuatorblock 29. The second rib 56 b is opposed to the upper end surface (firstend surface) 55 a of the second sleeve 52 and the outer peripheralsurface of the first rib 56 a with a slight gap therebetween, andfurthermore, is opposed to the inner peripheral surface of the innerhole 31 of the second actuator block 29 with a slight gap therebetween.

As above, a gap G of stepped-shape or of labyrinth-shape which extendsin the radial direction and the axis direction alternately is defined bythe first rib 56 a and the second rib 56 b between the upper and lowerbearing units 50. The gap G communicates with the gap between the upperand lower actuator blocks 29. FIG. 6 is a schematic cross-sectional viewshowing the gap G in a partly enlarged manner. As shown, grease leakingfrom two ball bearings 54 a and 54 b adjacent to the boundary of thefirst and second bearing units 50 must pass through the gap G, as shownwith a dotted line in the figure, to reach the gap between the upper andlower actuator blocks 29. As described above, the gap G as a passage ofthe grease (lubricant) is formed in a cranking manner or in alabyrinth-shape. That is, the gap G forms a long and complicatedpassage. Thus, the grease does not smoothly flow through the gap G andthe amount of grease reaching the gap between the actuator blocks 29significantly decrease. Thus, leakage and splashing grease from theboundary between the upper and lower actuator blocks 29 can beprevented. As described above, the gap G of a cranking manner or in alabyrinth-shape constitutes a seal structure which suppresses leakage oflubricant from the bearing unit to the outside of the first and secondactuator blocks.

As shown in FIG. 1, while the head actuator assemblies structured asabove are incorporated in the casing, the support shaft 26 is fixed tothe bottom wall 12 a and is disposed to be basically in parallel to thespindle of the spindle motor 19. Each magnetic disk 18 is disposedbetween the suspension assemblies 32. When the HDD is operated, thefirst and second actuator assemblies 22A and 22B are rotatedindependently from each other or integrally with each other, and themagnetic heads 17 attached to the suspension assembly 32 is opposed tothe upper surface and the lower surface of the magnetic disk 18. Thebase 42 of the FPC unit 21 is fixed to the bottom wall 12 a of the base12.

In the HDD and the actuator assembly structured as above, while aplurality of actuator assemblies which can independently drive arelayered, grease leaking from bearings of the bearing unit 50 andsplashing out can be suppressed and adhesion of grease to magnetic disksor magnetic heads can be prevented. Thus, a problem caused by adhesionof grease can be prevented and the HDD and the head actuator assembly ofgreat credibility can be achieved. Furthermore, the bearing units of thefirst and second actuator assemblies can have the same structure, andthus, the number of components of the actuator assembly can be reducedand the production costs can also be reduced.

Note that, in the first embodiment, the lower first rib 56 a ispositioned in the inner periphery side of the upper second rib 56 b inthe boundary of the upper and lower sleeves 52; however, no limitationis intended thereby. For example, the first and second ribs may bestructured such that the lower first rib 56 a is positioned on the outerperipheral side of the upper second rib 56 b. Furthermore, a gap ofstepped-shape or labyrinth-shape can be defined between the actuatorblocks 29 with similar first and second ribs as above.

Then, an HDD and a head actuator assembly of another embodiment will beexplained. In the following embodiment, structural elements as in thefirst embodiment will be referred to by the same reference numbers anddetailed description thereof may be omitted or simplified to focus ondifferences from the first embodiment.

Second Embodiment

FIG. 7 is a perspective view of an actuator block of a head actuatorassembly of HDD of the second embodiment where the actuator block isshown in a partly broken manner. FIG. 8 is a cross-sectional view of theactuator block of the head actuator assembly. FIG. 9 is a schematiccross-sectional view of a gap between bearing units.

In the second embodiment, in the head actuator assembly, a boundarybetween upper and lower bearing units has a structure different fromthat of the first embodiment. As shown in FIGS. 7 and 8, in the secondembodiment, a sleeve 52 of each bearing unit 50 includes, integrally, anannular first rib (first step) 56 a projecting from one end surfacethereof in the axis direction and an annular second rib (second step) 56b projecting from the other end surface thereof in the axis direction.The first rib 56 a is provided coaxially with the sleeve 52 and hassubstantially the same inner diameter as the inner diameter of thesleeve 52. The first rib 56 a has an outer diameter smaller than theouter diameter of the sleeve 52. The second rib 56 b is providedcoaxially with the sleeve 52 and has an inner diameter slightly greaterthan the outer diameter of the first rib 56 a. The outer diameter of thesecond rib 56 b is formed to be substantially the same outer diameter ofthe sleeve 52.

A second sleeve 52 of the second actuator assembly 22B is attached to asecond actuator block 29 while the first rib 56 a is located on theupper end side of the sleeve 52 and the second rib 56 b is located onthe lower end side thereof. A first sleeve 52 of the first actuatorassembly 22A is arranged upside down with respect to the second sleeve52, and thus, the first rib 56 a is located on the lower end side of thesecond sleeve 52 and the second rib 56 b is located on the upper endside thereof. Thus, the first rib 56 a of the first sleeve 52 and thefirst rib 56 a of the second sleeve 52 are opposed to each other in theaxis direction with a slight gap therebetween.

As shown in FIGS. 7, 8, and 9, an annular gap forming member (ring) 62is attached to the first sleeve 52 or the second sleeve 52. In thepresent embodiment, the ring 62 is fixed to the upper end of the secondsleeve 52 on the outer periphery side of the first rib 56 a. The ring 62has an inner diameter which is substantially the same as the outerdiameter of the first rib 56 a and an outer diameter which issubstantially the same as the outer diameter of the second sleeve 52.The ring 62 fit the outer periphery of the first rib 56 a and issubstantially flush with the outer peripheral surface of the secondsleeve 52. The upper half area of the ring 62 in the axis direction isformed to be narrower than the lower half area and constitutes anannular projection 62 a. The projection 62 a projects upward from theupper end surface of the second sleeve 52, that is, toward the firstsleeve 52. The projection 62 a overlaps the first rib 56 a of the firstsleeve 52 in a radial direction, that is, the projection 62 a and thefirst rib 56 a are positioned aside in the radial direction.Furthermore, the projection 62 a is opposed to the lower end surface ofthe first sleeve 52, outer peripheral surface of the first rib 56 a, andinner peripheral surface of the inner hole 31 of the first actuatorblock 29 with a slight gap therebetween.

As above, a gap G of stepped-shape or of labyrinth-shape which extendsin the radial direction and the axis direction alternately is defined bythe first rib 56 a and the ring 62 between the upper and lower bearingunits 50. The gap G communicates with the gap between the upper andlower actuator blocks 29. As shown in FIG. 9, grease leaking from twoball bearings 54 a and 54 b adjacent to the boundary of the first andsecond bearing units 50 must pass through the gap G to reach the gapbetween the upper and lower actuator blocks 29. As described above, thegap G as a passage of the grease is formed in a cranking manner or in amaze-like shape. Thus, the grease does not smoothly flow through the gapG and the amount of grease reaching the gap between the actuator blocks29 significantly decrease. Thus, splashing grease from the boundarybetween the upper and lower actuator blocks 29 can be prevented.

As explained above, in the second embodiment, the ring 62 as anindependent element is attached to the sleeve 52 to function as a rib.In the second embodiment, other components of the head actuator assemblyare the same as those of the head actuator assembly explained in thefirst embodiment. In the second embodiment structured as above, aproblem caused by adhesion of grease can be prevented and the HDD andthe head actuator assembly of great credibility can be achieved.Furthermore, the bearing units of the first and second actuatorassemblies can have the same structure except for the ring 62, and thus,the number of components of the actuator assembly can be reduced and theproduction costs can also be reduced.

Note that, in the second embodiment, the ring 62 is disposed on theouter periphery of the lower first rib 56 a in the boundary of the upperand lower sleeves 52; however, no limitation is intended thereby. Forexample, the ring 62 may be disposed on the outer periphery of the upperfirst rib 56 a. Furthermore, the first rib 56 a may be located on theouter periphery side of the sleeve 52 and the ring 62 may be disposed onthe inner periphery side of the first rib 56 a.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the inventions. Indeed, the novel embodiments described hereinmay be embodied in a variety of other forms; furthermore, variousomissions, substitutions and changes in the form of the embodimentsdescribed herein may be made without departing from the spirit of theinventions. The accompanying claims and their equivalents are intendedto cover such forms or modifications as would fall within the scope andspirit of the inventions.

For example, in the above embodiments, a gap between upper and lowerbearing units opposed to each other is formed in a stepped-shape or alabyrinth-shape by combining a first rib provided with one sleeve and asecond rib or a ring provided with the other sleeve. Or, for example, agag G of further complicated shape may be defined by a plurality ofannular ribs (steps) which are apart from each other in a radialdirection provided with sleeves wherein the ribs of one sleeve comebetween the ribs of the other sleeve with gaps therebetween.

Furthermore, the actuator assembly is not limited to the above first andsecond assemblies, and three or more actuator assemblies may berotatably supported on a common axis. In that case, the aforementionedgap of stepped-shape or labyrinth-shape may be provided with a gapbetween adjacent the upper and lower sleeves.

The number of the magnetic disks is not limited to seven, and it may besix or less, or may be eight or more. The number of the suspensionassemblies and the number of magnetic heads can be increased dependingon the number of disks adopted.

What is claimed is:
 1. A disk device comprising: a recording medium; afirst actuator assembly including a first actuator block rotatablysupported on a support shaft via a first bearing unit, and a firstsuspension assembly extending from the first actuator block andincluding a first magnetic head; and a second actuator assemblyincluding a second actuator block rotatably supported on the supportshaft via a second bearing unit, and a second suspension assemblyextending from the second actuator block and including a second magnetichead, wherein the first bearing unit comprises a first sleeve fixed tothe first actuator block and located around the support shaft, and afirst ball bearing disposed between the support shaft and the firstsleeve, the second bearing unit comprises a second sleeve fixed to thesecond actuator block and located around the support shaft, and a secondball bearing disposed between the support shaft and the second sleeve,the first sleeve includes a first end surface opposed to the secondsleeve, the second sleeve includes a second end surface opposed to thefirst end surface with a gap therebetween, and at least one of the firstend surface and the second end surface includes an annular rib.
 2. Thedisk device of claim 1, wherein each of the first end surface and thesecond end surface includes an annular rib, and the annular rib of thefirst end surface overlaps the annular rib of the second end surfacewith a gap in a radial direction of the first sleeve.
 3. The disk deviceof claim 2, wherein the gap between the first end surface and the secondend surface has a labyrinth-shape.
 4. The disk device of claim 1,wherein at least one of the first bearing unit and the second bearingunit includes a ring member which is attached to at least one of thefirst sleeve and the second sleeve and forms the annular rib.
 5. A diskdevice comprising: a recording medium; a first actuator assemblyincluding a first actuator block rotatably supported on a support shaftvia a first bearing unit, and a first suspension assembly extending fromthe first actuator block and including a first magnetic head; and asecond actuator assembly including a second actuator block rotatablysupported on the support shaft via a second bearing unit, and a secondsuspension assembly extending from the second actuator block andincluding a second magnetic head, wherein the first bearing unitcomprises a first sleeve fixed to the first actuator block and locatedaround the support shaft, and a first ball bearing disposed between thesupport shaft and the first sleeve, the second bearing unit comprises asecond sleeve fixed to the second actuator block and located around thesupport shaft, and a second ball bearing disposed between the supportshaft and the second sleeve, the first sleeve includes a first endsurface opposed to the second sleeve, the second sleeve includes asecond end surface opposed to the first end surface with a gaptherebetween, and the gap is formed in a labyrinth-shape.
 6. A diskdevice comprising: a recording medium; a first actuator assemblyincluding a first actuator block rotatably supported on a support shaftvia a first bearing unit, and a first suspension assembly extending fromthe first actuator block and including a first magnetic head; and asecond actuator assembly including a second actuator block rotatablysupported on the support shaft via a second bearing unit, and a secondsuspension assembly extending from the second actuator block andincluding a second magnetic head, wherein the first bearing unitcomprises a first sleeve fixed to the first actuator block and locatedaround the support shaft, and a first ball bearing disposed between thesupport shaft and the first sleeve, the second bearing unit comprises asecond sleeve fixed to the second actuator block and located around thesupport shaft, and a second ball bearing disposed between the supportshaft and the second sleeve, the first sleeve includes a first endsurface opposed to the second sleeve, the second sleeve includes asecond end surface opposed to the first end surface with a gaptherebetween, and at least a part of the second sleeve overlaps at leasta part of the first sleeve in a radial direction of the first sleeve. 7.The disk device of claim 6, wherein the first sleeve includes a firstend portion including the first end surface and the second sleeveincludes a second end portion including the second end surface, and atleast a part of the first end portion overlaps at least a part of thesecond end portion with a gap in the radial direction.
 8. The diskdevice of claim 6, wherein at least one of the first end surface and thesecond end surface includes an annular rib.
 9. The disk device of claim8, wherein each of the first end surface and the second end surfaceincludes an annular rib.
 10. The disk device of claim 9, wherein theannular rib of the first end surface overlaps the annular rib of thesecond end surface with a gap in the radial direction of the firstsleeve.